kubeadm: add default paths to 'upgrade diff'

After the flags to control manifest paths were removed,
the variables in diff.go remained empty and the validation
fails with "empty manifest path".

Always populate the paths with the kubeadm defaults under
/etc/kubernetes/manifest and remove the empty path validation.

Author: neolit123

cmd/kubeadm/app/cmd/upgrade/diff.go

@@ -57,8 +57,11 @@ type diffFlags struct {
 // newCmdDiff returns the cobra command for `kubeadm upgrade diff`
 func newCmdDiff(out io.Writer) *cobra.Command {
 	flags := &diffFlags{
-		kubeConfigPath: constants.GetAdminKubeConfigPath(),
-		out:            out,
+		kubeConfigPath:                constants.GetAdminKubeConfigPath(),
+		out:                           out,
+		apiServerManifestPath:         constants.GetStaticPodFilepath(constants.KubeAPIServer, constants.GetStaticPodDirectory()),
+		controllerManagerManifestPath: constants.GetStaticPodFilepath(constants.KubeControllerManager, constants.GetStaticPodDirectory()),
+		schedulerManifestPath:         constants.GetStaticPodFilepath(constants.KubeScheduler, constants.GetStaticPodDirectory()),
 	}
 
 	cmd := &cobra.Command{
@@ -88,9 +91,6 @@ func newCmdDiff(out io.Writer) *cobra.Command {
 
 func validateManifestsPath(manifests ...string) (err error) {
 	for _, manifestPath := range manifests {
-		if len(manifestPath) == 0 {
-			return errors.New("empty manifest path")
-		}
 		s, err := os.Stat(manifestPath)
 		if err != nil {
 			if os.IsNotExist(err) {

cmd/kubeadm/app/cmd/upgrade/diff_test.go

@@ -113,13 +113,6 @@ diff:
 			cfgPath:       "missing-path-to-a-config",
 			expectedError: true,
 		},
-		{
-			name:            "invalid: valid config but empty manifest path",
-			cfgPath:         testUpgradeDiffConfig,
-			setManifestPath: true,
-			manifestPath:    "",
-			expectedError:   true,
-		},
 		{
 			name:            "invalid: valid config but bad manifest path",
 			cfgPath:         testUpgradeDiffConfig,